The inventive concepts disclosed herein generally relate to the field of control panel illumination.
Current lighted switch panels (i.e. “keypanels”) in aircraft typically use either incandescent lighting or LED lighting. Incandescent lighting is unreliable and requires high power (>12 Watts). Additionally, incandescent lighting requires fragile, expensive “flex” cables to connect to the backlight driver. LED lighting has been used to reduce power and improved reliability, but can require complex and expensive waveguides to provide adequate illumination characteristics, as well as to match a dimming curve of an incandescent lighting scheme. For example, designing and implementing waveguides to direct and balance the keypanel illumination can often be time consuming and expensive, customized tuning is required for each application. Further, the need for a waveguide adds unnecessary thickness to the keypanel assembly, which consumes critical space in a cockpit of an aircraft. In addition, due to the use of common waveguides, it is often difficult to individually illuminate a single key or symbol due to the illumination passing through the common waveguide from multiple LEDs. Further, instead of only illuminating a specific symbol, the use of a common waveguide can cause the level of illumination to vary between different keys or symbols of the keypad, depending on the location of the particular LED providing the illumination. Finally, the use of a common waveguide can make it difficult to illuminate individual portions of the keypanel with different colors, as the common waveguide can cause the different colored illuminations from multiple LEDs to blend together, making tuning individual colors on the keypanel difficult.
Vehicle crewstations and cockpits generally include multiple display and control panels, each with their own lighting. This lighting is generally provided within each display and/or control panel by incandescent lighting or LED lighting. A filter is generally applied to the respective light source to limit the infrared emissions to prevent or reduce interference with a crew's night vision-system, such as night vision goggles (“NVG”). This type of lighting is generally referred to as “panel lighting.” Additionally, the crew generally uses a dimming device, such as a rheostat or variable voltage source to adjust the panel lighting brightness. This voltage is generally connected to all control and display units. Since all devices generally use the same kind of lighting device, the brightness among the control and display units generally tracks as the dimming level is adjusted.
In addition to panel lighting, crewstations and cockpits can use multifunction displays (“MFDs”) to display essential information. MFDs generally use large-active-area cathode ray tubes (“CRT”) or liquid crystal displays (“LCDs”) to convey information. These displays generally vary in size from 3″×3″ to 8″×20.″ Since LCDs are a transmissive technology and do not emit light, LCD based MFDs are generally illuminated by a backlight device, such a fluorescent lamps or LEDs, located behind the display.
MFDs typically have illuminated switch panels around the periphery of the CRT or LCD. These panels may have “hard keys,” such as rotary knobs or pushbuttons with dedicated functions. The panes may also include “soft keys,” which allow for variable functions. Hard keys provide rapid single-action access to major, critical functions. Soft keys are labeled by software in the MFD that draws a word or symbol adjacent to the soft key on the display, to label its functions. A soft key may take on many different functions depending on the MFD software. This allows each soft key to replace hundreds of fixed function switches, thereby significantly reducing the cockpit or crewstation area needed for controls. The use of soft keys in conjunction with MFDs can allow for substantial growth in functions, without adding new control or MFD panels.
Each MFD typically has a brightness control for the display, separate from instrument panel lighting. This is necessary to allow the crew to balance the large, bright display area with the instrument panel lighting for optimum viewing ability under the current lighting conditions. The switch panel brightness is controlled by an instrument panel dimming device.
Furthermore, vehicles such as aircraft must operate under a wide range of lighting environments. Ambient illumination can vary from 0.1 fc to 10,000 fc or more. To accommodate the changes in illumination as the vehicle moves, some MFDs use automatic brightness control (“ABC”). ABC works by measuring the light falling on the switch panel and increasing the LCD or CRT brightness as the ambient illumination increases. This can help to keep the display from “washing out” and losing contrast in bright sunlight.
Illuminated keypanels have been proposed for use in aviation and are discussed in U.S. Pat. Nos. 7,492,356 and 8,232,492, all assigned to the assignee of the present application and incorporated in their entireties herein by reference.
Accordingly, current systems and methods of backlighting avionic keypanels and/or keypads can be unreliable, complex and expensive due to custom requirements for different types of aircraft or other applications. Thus, a simple and cost-effective method of providing backlight to avionic keypanels and/or keypads may be desirous.